It might just be the best deal ever offered by the city to the uninsured: a completely free prescription-drug discount card with savings averaging 47 percent off retail prices that’s available to everyone.

“Today, we are pleased to bring all uninsured and underinsured New Yorkers a dose of very good news,” Mayor Bloomberg declared at a press conference with City Council Speaker Christine Quinn at the Target outlet in Downtown Brooklyn.

He explained that the card, which took the city six years to produce, is valid at 85 percent of the city’s pharmacies and comes with no catches for the 1.2 million people here without medical insurance.

There’s no charge to apply for or use the card and it can be used by an entire family.

“All too often, the rising costs of prescription drugs place a burden on New York City households. And this is particularly true for the more than 1 million New Yorkers who don’t have health insurance,” said Bloomberg.

The savings can be phenomenal — 53 percent on average for generic drugs and 15 percent for name brands.

It doesn’t cost taxpayers a cent because the distributor, Health Trans Access, is picking up all marketing costs and other expenses.

The one caveat offered by the mayor was that the card can’t be used in combination with insurance or other discounts.

Although there are similar programs around the country — Nassau County started one back in 2004 — Bloomberg had a hard time convincing reporters there was no downside.

“You just get the card. What could be simpler?” he told one skeptical reporter.

Another reporter asked how pharmacies could possibly offer such huge discounts.

“They have a very high profit margin,” said the mayor. “There’s no secrets here.”

In fact, the margins on some drugs border on the ludicrous.

One official said the generic version of the cholesterol drug Zocor is priced at an average of $69.61 retail in the city. With the card, it goes for $18.51 — a startling but welcome 75 percent discount.

The Health Department first tried to launch a discount-prescription program in 2005, only to find that just one vendor responded to its Request For Proposal. When that vendor wanted the city to chip in money for publicity and marketing, the agency went back to square one before signing Health Trans Access.

Deputy Mayor Linda Gibbs said New Yorkers should have confidence this is one deal that, while it sounds too good to be true, actually is legitimate.

“This is not a scam,” she said.

The discount card can be downloaded at BigAppleRx.com or it can picked up at local businesses and community groups.